Groundwater arsenic content in Raigón aquifer system (San José, Uruguay)

As a Medical Geology research issue, an environmental arsenic risk assessment study in the most important sedimentary aquifer in southern Uruguay is presented. The Raigón Aquifer System is the most exploited in Uruguay. It has a surface extent of about 1,800 square kilometres and 10,000 inhabitants in San Jose Department, where it was studied. Agriculture and cattle breeding are the main economic activities and this aquifer is the basic support. The groundwater sampling was done on 37 water samples of PRENADER (Natural Resources Management and Irrigation Development Program) wells. Outcropping sediments of Raigón Formation and the overlying Libertad Formation were also sampled in the Kiyú region. The analyses were performed by inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS). The results showed 80% samples with arsenic levels exceeding the 10 μg/l of WHO as limit for waters, and 11% exceeds the 20 μg/l limit of uruguayan regulation. The median, maximum and minimum water arsenic concentrations determined have been 14.24, 24.19 and 1.44 μg/l, respectively. On the other hand, nine sediment samples of Raigón and Libertad Formations in Kiyú region were analysed and yielded median, maximum and minimum arsenic concentrations of 5.03, 9.82 and 1.18 ppm, respectively. This issue leads to the supposition that the population, as well as industrial and agricultural activities, are consuming water with arsenic concentrations over the national and international maximum recommended limit.Como una aproximación a la Geología Médica en Uruguay se presentan los resultados de un estudio sobre el estado del Sistema Acuífero Raigón en relación a la presencia de arsénico, en el entendido que es el acuífero más explotado en el país. En particular, el área cubierta por este trabajo es de unos 1800 km2 en un territorio con una población de unos 10,000 habitantes en el departamento de San José. La colecta de aguas del acuífero se realizó en perforaciones de la base de datos de PRENADER (Proyecto de Manejo de Recursos Naturales y Desarrollo del Riego) obteniéndose 37 muestras, y sobre 9 muestras de sedimentos tanto de la Formación Raigón como la suprayacente Libertad en afloramientos de la región de Kiyú. Los análisis fueron realizados mediante ICP-MS. Un 80% de las muestras de aguas analizadas mostraron contenidos mayores a los límites de la OMS (10 μg/l) y un 11% de las muestras superaron el límite de la OSE (20 μg/l). El valor medio, máximo y mínimo determinado en el caso del agua subterránea fue de 14.24, 24.19 and 1.44 μg/l, respectivamente. Por otro lado, las nueve muestras de sedimentos analizados mostraron concentraciones media, máxima y mínima de arsénico de 5.03, 9.82 and 1.18 ppm, respectivamente, descartándose en principio un origen geogénico.Cooperation between the University of the Republic (Uruguay) and CSIC from Spain (Ref. 2005UY0001). DINACYT-Uruguay, Project of the Technological Development Program PDT # 45/14 which included the doctoral thesis work of MSc. Rosario Guerequiz. CYTED Iberoarsen Network and the International Medical Geology Association contributed with scientific and technical support to improve the knowledge on environmental arsenic and health impacts, with a multidisciplinary approach in Uruguay. This work was performed under the Research Consolidated Groups SGR-2005-795 PEGEFA (Petrology and Geochemistry Basic and Applied) and SGR-2005-00589 (Mineral Resources), funded by AGAUR-DURSI, Generalitat de Catalunya.Peer reviewe